Every child is different. I have a daughter and two sons, all of whom were introduced to shooting at very early ages. They all started out with BB guns, graduated to air rifles, then to .22s and on up. I don't recall exactly what age each was when they first shot "real guns," but I started them out as early as I could, given their level of interest, strength, coordination, and focus. I have a photo of my younger son hunkered down behind a short AR on a bipod, when he was barely 5 years old. All of mine had shot a Model 63 Smith by the age of 5 and the boys had done it by between 3 and 4, with careful guidance by me.
My daughter and my boys went with me on dove hunts before they were old enough to shoot shotguns, and they loved it. I did, too, and they made great bird dogs! They helped me clean the birds, too. As soon as they were big enough to handle them, I bought the boys 20 ga. Remington Youth Model 870s, which they learned to shoot well over my little Outers trap before hitting the fields for doves, quail and pheasants. (My daughter, by that time, had lost most interest in hunting, but still loved to shoot, and to eat what the boys and I killed.)
I took my boys deer hunting for the first time when they were 10 and 12, with my older son using my old Ruger Model 77 .243 and my younger one an AR. My older boy shot a nice buck, my younger one missed a chance, but not a shot, at another, I killed a small buck, and we all collected treasured memories.
All my kids came along with my wife and me to USPSA pistol and 3-gun matches, beginning when my daughter was 3 and my older son was a baby.
My kids now range in age from 24 to 28, and all are still frequent and skilled shooters. My daughter has three kids and one on the way, and the older two of hers (7 and almost 5) both are being taught by their dad on a Chipmunk .22 I bought them. I expect that my granddaughter will soon get her first experience with the Model 63 I gave to my son-in-law, to allow him to do what I did.
I've seen kids that were not really ready for much instruction on firearms until they were 7 or 8 years old, but they're the exception. Firehouse, you are to be commended for starting your boy out at a young age, and for your dedication to making him a shooter. If those of your generation and mine don't help bring along the next one, the Second Amendment and all that goes with it, including the joys of shooting and hunting with family, will become nothing but the memory the antis want it to be.